1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a heat exchanger that is designed to reduce flow-resistance of air introduced into a fin collar region of a corrugate fin and to provide a uniform airflow speed distribution to the fin.
2. Description of the Related Art
Generally, a heat pump type air conditioner is operated in a cooling mode when an indoor temperature is higher than a predetermined level and is operated in a heating mode when the indoor temperature is lower than the predetermined level. At this point, when the air conditioner is operated in the heating mode, a heat exchanger of the air conditioner functions as an evaporator.
FIG. 1 shows a conventional heat pump type air conditioner.
Referring to FIG. 1, the heat pump type air conditioner is operated in cooling and heating modes according to an indoor temperature.
In the cooling mode, refrigerant gas pumped out from a compressor 1 is separated from oil while passing through an oil separator 2, which is then directed to an outdoor heat exchanger 4 through a four-way valve 3. The refrigerant gas directed to the outdoor heat exchanger is phase-transited into a low-temperature low-pressure state while passing through an expansion valve 5 and is then directed to an indoor heat exchanger 6. The refrigerant gas vaporized in the indoor heat exchanger 6 is heat-exchanged with indoor air and is then directed to an accumulator 7 through the four-way valve 3. The refrigerant gas directed to the accumulator 7 is directed into the compressor 1 for the same circulation.
In a heating mode, the refrigerant gas pumped out from the compressor 1 is separated from oil while passing through the oil separator 2, which is then directed to the indoor heat exchanger 6 through the four-way valve 3 to thereby be condensed to heat-exchange with indoor air. The condensed refrigerant gas is then changed into a low-temperature low-pressure state while passing through the expansion valve 5 and is vaporized while passing through the heat exchanger 4. The vaporized refrigerant gas is directed to the accumulator 7 through the four-way valve 3. The refrigerant gas directed to the accumulator 7 is directed into the compressor 1 for the circulation.
FIG. 2 shows a conventional heat exchanger 4, and FIG. 3 shows a state where frost is formed on a surface of a fin.
Referring to FIGS. 2 and 3, the heat exchanger 4 includes a heat exchanging member 8 for performing a heat exchange between the refrigerant and outdoor air, a blower fan 9 for sucking and discharging the outdoor air for the heat exchange of the heat exchanging member 8.
At this point, the outdoor air discharged by the blower fan 9 passes through an air passage defined between flat fins 11 fixed on tubes 10. In the heating mode, frost is formed on the surfaces of the fins 11 fixed on the tube 10. Here, the frost 12 formed on the flat fins 11 is relatively thick at the front end of the flat fin 11 where a relatively large amount of air flows, and the thickness of the frost 12 is gradually reduced as it goes toward a rear end of the flat fin 11.
The heat exchangers 8 are classified into several types according to a type of cooling fin arranged on the tubes. Most widely used is a corrugate fin type.
FIG. 4 shows a conventional corrugate fin type heat exchanger.
Referring to FIG. 4, a heat exchanger 101 includes a plurality of W-shaped corrugate fins 110 spaced away from each other at a predetermined distance and a plurality of tubes disposed perpendicularly penetrating the corrugate fins 110. Refrigerant flows along the tubes 130.
The fin 110 includes peak and valley portions 112 and 114 that are alternately formed on a region, where the tubes 130 are not penetrating, and connected to each by longitudinal inclined sections, fin collars 116 through which the tubes 130 are inserted, longitudinal axes of the tubes being perpendicularly penetrating a longitudinal centerline of the fin 110, and seat portions 118 for supporting the fin collars 116.
The heat exchanger having such corrugate fins will be described more in detail hereinafter with reference to FIGS. 4 to 7.
Referring to FIG. 4, the heat exchanger 101 is a fin-tube type having the plurality of fins 110 through which two rows of tubes 130 penetrate at right angles.
Each of the fins 110 has a plurality of donut-shaped flat portions and a plurality of longitudinal inclined sections that are defined by the W-shape having a plurality of the peak and valley portions 112 and 114. The fins 110 are installed on the tubes 130 in a longitudinal direction of the tubes 130, being spaced away from each other at a predetermined distance.
Referring to FIGS. 5 and 6, there is shown a detailed structure of the fin 110. The fin 110 is formed having a W-shape with the peak and valley portions 112 (112a and 112b) and 114 (114a, 114b and 114c) that are alternately formed. That is, the fin 110 has two side ends that are respectively defined by the valley portions 114a and 114c. The fin 110 can be formed in a multiple fin structure combining a plurality of fins to each other side by side. In order to improve the heat exchange efficiency, the tubes are arranged in a zigzag-shape.
That is, each of the fins 110 installed on the tube 130 has two peak portions 112a and 112b and three valley portions 114a, 114b and 114c, which are alternately disposed and connected by inclined sections. The shape of the fin 110 is symmetrical based on the longitudinal center valley portion 114b. Central axes of the tube 130 pass through the longitudinal center valley portion 114b. 
The fin 110 is provided with a plurality of tube insertion holes 116a, whose central axes correspond to the respective central axes of the tubes 130. The fin collars 116 are elevated from the fin 110 to define the tube insertion holes 116a through which the tubes 130 are inserted. The tube 130 surface-contacts an inner circumference of each fin collar 116. The seat portion 118 is formed around a lower end of an outer circumference of the fin collar 116 to support the fin collar 116 and to allow air to flow in the form of enclosing the tube 130 and the fin collar 116.
An inclined portion 120 is formed on the fin 110 around the seat portion 118 to prevent the air flowing around the tube 130 from getting out of a circumference of the tube 130. The inclined portion 120 is inclined upward from the seat portion 18 to the peak portions 112.
In addition, the seat portion 118 is located on a horizontal level identical to that where the valley portions 114 are located. Heights and depths H1 of the peak and valley portions 112 and 114 are identical to each other. In addition, the inclined angles of the longitudinal inclined sections connecting the valley portions to the peak portions are also identical to each other.
When the air is introduced into the heat exchanger 101, since the seat portions 118 and the valley portions 114 are located on an identical horizontal plane, the air flowing around the tubes cannot reach the rear ends of the tubes. In addition, the growth of frost formed on an outer surface of the fin 110 is proportional to an amount of a heat transfer on the outer surface of the fin 110. The airflow speed is increased at the fin regions between the tubes, thereby forming a high-speed airflow. As a result, the heat transfer coefficient is increased and the frost layer is quickly grown on the surface of the fin 110 as shown in FIG. 3.
When the frost layer is grown on the surface of the fin 110, since the distance between the adjacent fins 110 is reduced, an air passage area is also reduced. By the reduced area, the airflow speed is increased, as the result of which the pressure drop of the air is increased in the form of a parabola as time elapses and the heat transfer amount of the heat exchanger is also greatly reduced.
In addition, the air flowing around the tubes is accumulated at the rear ends of the tubes, deteriorating the heat transfer efficiency. That is, since the seat portions and the valley portions are located on the identical horizontal plane, the air cannot sufficiently reach the rear ends of the tubes. As a result, a wake region where the air is accumulated is formed on the rear ends, thereby deteriorating the heat transfer efficiency.
Therefore, there is a need for guiding high-speed airflow up to the rear ends of the tubes where the wake region is formed.